ELECTRIC MOTOR FOR A MOTOR VEHICLE

Description

Title Electric motor for a motor vehicle DESCRIPTION ELECTRIC MOTOR FOR A MOTOR VEHICLE 'k 'k 'kkkkkkk The present invention relates to an electric motor for a motor vehicle. There are known electric or hybrid powered vehicles, which include a permanent magnet electric motor. In short, the permanent magnet electric motor includes, in turn: - a stator equipped with electrical windings that can be electrically energized to form a rotating magnetic field; and - a rotor mounted so as to rotate relative to the stator around its own axis, and equipped with permanent magnets and subjected to a driving torque around the axis as a result of the electrical windings being supplied with alternating current. The industry is keenly aware of the need to cool the electric motor, reducing its overall weight and size. There is also a perceived need in the sector to increase the torque and power density - i.e. the ratio between torque / power and weight - of the electric motor. The aim of the present invention is to create an electric motor for a motor vehicle which can satisfy at least one of the above-mentioned requirements. The above-mentioned object is achieved by the present invention, since it relates to an electric motor as defined in claim 1. For a better understanding of the present invention, a preferred embodiment is described below, by way of non-limiting example and with reference to the attached drawings in which: - figure 1 is a cross-section of an electric motor made according to the dictates of the present invention; - Figure 2 is a perspective view of the first components of the electric motor of Figure 1; - Figure 3 is a perspective view of second components of the electric motor of Figure 1; and - figure 4 shows a perspective view and a section along a longitudinal plane of a rotor of the electric motor of figures 1 to 3. With reference to Figure 1, the number 1 indicates an electric or hybrid powered motor vehicle 1. The motor vehicle 1 is illustrated with only one electric motor 2, a permanent magnet electric motor in the case illustrated, The electric motor 2 essentially comprises: - a stator 3 fixed with respect to an axis A; and - a rotor 4 rotating around axis A with respect to stator 3. In a known manner, the stator 3 is provided with electrical windings (not illustrated in Figure 1) which are electrically supplied with an electric current to form a rotating magnetic field. Rotor 4 is equipped with permanent magnets (also not shown in Figure 1) and is subjected to a driving torque about axis A as a result of the electrical windings being supplied with alternating current. In the case illustrated, the stator 3 is tubular with axis A and the rotor 4 is housed coaxially inside the stator 3. Stator 3 comprises, in turn: - a main body 10; and - a pair of appendages 11, 12 arranged at respective axial ends of the main body 10. The appendages 11, 12 protrude axially from the main body 10. The main body 10 is delimited by a radially external surface 13 and a radially internal surface 14. The appendages 11, 12 are radially interposed between the surfaces 13, 14 and connected to the surfaces 13, 14 themselves by means of respective shoulders 16, 17. Rotor 4 comprises, in turn: - a main body 20 housed inside the stator 3 and delimited by a surface 21; and - a pair of appendages 22, 23 arranged at respective opposite axial ends of the main body 20 and protruding radially from the main body 20 itself. The appendages 22, 23 are connected to the surface 21 themselves by means of respective shoulders 24, 25. The electric motor 2 also includes: - a casing 30 of axis A, fixed with respect to axis A and coaxially housing the stator 3 and the rotor 4; and - a pair of radially rotating bearings 40, 41 interposed between the rotor 4 and the casing 30, and designed to allow the rotation of the rotor 4 around the axis A with respect to the casing 30. The casing 30 is shaped like a hollow cylinder and essentially comprises: - a tubular wall 31 with a predominantly axial development; and - a pair of flanges 32, 33 arranged at respective axial ends of the wall 31. Each flange 32, 33 comprises: - a respective hole 38 of axis A crossed with radial clearance by a respective appendage 22, 23 of rotor 4; and - a respective shoulder 35 delimiting the corresponding hole 38 in a radially internal position with respect to the axis A. Each bearing 40 is radially interposed between a respective appendix 22, 23 and the shoulder 35 defined by a corresponding flange 32, 33. Advantageously, the electric motor 2 comprises a cooling circuit 50 which can be passed through by a first heat-transfer fluid, in particular dielectric oil, and which is thermally coupled with the stator 3 and the rotor 4 to remove heat from them; the cooling circuit 50 comprises, in turn, a branch 51 housed inside the said rotor 4 and shaped like a propeller. The motor vehicle 1 also comprises a cooling circuit 60 which can be passed through by a second heat transfer fluid, in particular water with glycol, and which is thermally coupled with the cooling circuit 50 to remove heat from it. In very summary, the cooling circuit 50 removes heat from the stator 3 and the rotor 4, and the cooling circuit 60 removes heat from the cooling circuit 50. In more detail, the cooling circuit 50 is integrated into the electric motor 2. The cooling circuit 50 also includes: - a branch 52 passing through the stator 3; and - a branch 53, which fluidly connects branches 51, 52; - a branch 54 crossing the casing 30; and - a branch 55 fluidly connecting branch 54 and branch 51. In more detail, the first fluid advances sequentially along branch 51, branch 53, branch 52, branch 54, branch 55 and then returns to branch 51. As will be clear from the remainder of this description, the advancement of the first fluid is caused by the thrust provided by the rotor 4 to the first fluid present in the branch 51. Preferably, the cooling circuit 50 does not include drive pumps to determine the advancement of the first fluid. With particular reference to Figure 4, the rotor 4 comprises: - a helical groove 66 of axis A, preferably with constant pitch and defined on the main body 20; and - a pair of ducts 67, 68 also with axis A, arranged in correspondence with respective axial ends opposite each other of the groove 66 and defined by respective appendages 23, 22. Branch 51 includes: - a section 69 defined by the groove 66; and - a pair of axial sections 61, 62 defined by respective ducts 67, 68. Sections 61, 62 are in fluid connection with branches 52, 54 of the cooling circuit 50 respectively. The sections 61, 62 are arranged in correspondence with respective axial ends opposite each other of the section 69. The section 69 and the groove 66 are shaped so that the centrifugal force acting on the first fluid following the rotation of the rotor 4 in a first direction determines an axial thrust on the first fluid having a second direction oriented from the section 62 to the section 61. The electric motor 2 also includes: - a radial hole 68, passing through the appendix 23, and in fluid communication with the duct 67; - an annular chamber 70 in fluid communication with the hole 68; - an annular chamber 75, housing the stator 3 and in fluid communication with the chamber 70; a helical groove 80 in fluid communication with the chamber 75; - a radial duct 85 passing through and in fluid communication with the groove 80 and the chamber 75; and - a conduit 90 extending radially from the axis A, and extending from an axial end of the groove 80 opposite the hole 85 to the conduit 68. In particular, the casing 30 comprises an appendix 28 projecting cantilevered from the flange 32 towards the rotor 4 and an appendix 29 projecting cantilevered from the flange 33 towards the appendix 28. Appendices 28, 29 are axially opposed to each other. Appendix 28 includes, in particular: - an axially developed wall 36, extending from the flange 32 and radially interposed between the wall 31 and the appendix 22; and - a radially developed wall 37, axially interposed between the flange 32 and the main body 20, and extending radially between an axial end of the wall 36 axially opposite the flange 32 and the appendix 22. The appendix 29 is tubular, surrounds the shoulder 35 at a radial distance and is arranged at the same radial distance from the axis A of the wall 36. In particular, wall 37 is separated by a radial clearance from appendix 22. The casing 30 also comprises an annular element 76 fixed to the wall 36 and to the appendix 28 and interrupted in correspondence with a plurality of radial holes 39 (only one of which is illustrated in Figure 1) obtained in the wall 36 itself. Chamber 70 is delimited axially between flange 32 and wall 37 and radially between wall 36 and appendix 22. Chamber 75 is axially delimited between flanges 32, 33, and is radially delimited between casing 30 and member 76 and appendix 28. Chamber 75 is in fluid communication with chamber 70 through a plurality of holes 39 (only one of which is illustrated in Figure 1). The hole 85 and the groove 80 are obtained inside the wall 31 of the casing 30. The duct 90 is obtained in the flange 33 and comprises, in turn, proceeding from the groove 80 towards the duct 68: - a 91 section; and - a chamber 92 having a radial dimension greater than the section 91. The branches 53; 52 of the cooling circuit 50 are defined respectively by the hole 68 and the chamber 70; and by the chamber 75. The branches 54, 55 of the cooling circuit 50 are defined by the groove 80 and the duct 90 respectively. The cooling circuit 60 is partly housed inside the motor vehicle 1. The cooling circuit 60 comprises, in turn, only schematically illustrated in Figure 1: - a 100 pump; and - a radiator 102. The pump 100 includes a suction port 103 and a delivery port 104 and can be operated to generate the head necessary to advance the second fluid along the cooling circuit 60. The cooling circuit 60 comprises, in turn, proceeding from the delivery mouth 104 to the suction mouth 103 according to the direction of flow of the second fluid: - a branch 105 external to the electric motor 2 and along which the second fluid flows at a first temperature; - a branch 106 obtained inside the electric motor 2 and along which the second fluid removes heat from the first fluid, until it reaches a second temperature value higher than the first temperature value; and a branch 107 external to the electric motor 2. The radiator 102 is interposed along the branch 107 and brings the temperature of the second fluid from the second value to the first value by exchanging heat with a cold source. The pump 100 and the radiator 102 are carried by the motor vehicle 1 externally to the electric motor 2. The wall 31 of the casing 30 further comprises: - an inlet port 110 fluidically connected to branch 105 of the cooling circuit 60; - an outlet 111 fluidically connected to the branch 107 of the cooling circuit 60; and - a 115 helical groove of axis A. Wall 31 also includes: - the inlet duct 67, which develops radially and extends between the inlet mouth 110 and an inlet 117 of the groove 115; and - the outlet duct 68, which develops radially and extends between an outlet 118 of the groove 115 and the outlet mouth 111. Groove 115 is housed coaxially within groove 80. Branch 106 is defined by conduit 116, groove 115 and conduit 120. Branches 106, 54 of the respective cooling circuits 60, 50 are radially facing each other inside the casing 30. Branches 106, 54 are thermally coupled so that the first fluid flowing within branch 54 transfers heat to the second fluid flowing within branch 106. In use, the drive of the electric motor 2 causes heat to be generated at the rotor 4 and stator 3. Due to the presence of permanent magnets, heat generation is greatest at rotor 4. The first fluid flows inside the cooling circuit 50, carrying heat away from the rotor 4 and the stator 3 and overheating. The second fluid flows inside the cooling circuit 60 removing heat from the first cooling fluid and thus allowing the aforementioned first fluid to continue removing heat from the rotor 4 and the stator 3. In greater detail, the pump 100 determines the advancement of the second fluid inside the cooling circuit 60 in a direction oriented from the suction port 103 to the delivery port 104. The second fluid flows along the branch 105 external to the electric motor 2 at the third temperature value, reaches the inlet port 110, flows along the branch 106 internal to the electric motor 2 and removes heat from the first fluid until it reaches the fourth temperature value higher than the third temperature value, exits the electric motor 2 via the outlet port 111 and returns to the pump 100 via the branch 107 external to the electric motor 2. The second fluid passes through the radiator 102 and cools until it returns to the third temperature value. At the same time, the rotation of the rotor 4 around the axis A determines, thanks to the fact that the section of the branch 51 is defined by the helical groove 66, an axial thrust on the first fluid which allows it to advance inside the cooling circuit 50 in the direction oriented from the duct 67 to the duct 68 without requiring the use of further motor parts. More specifically, the helical shape of the groove 66 allows the centrifugal force due to the rotation of the rotor 4 around the axis A to be used to create an axial force parallel to the axis A which pushes the second fluid inside the cooling circuit 50. The first fluid cools the rotor 4 by flowing inside the duct 67, the groove 66 and the duct 68, which define respective sections 61, 69, 62 of the branch 51. Subsequently, the first fluid passes through the hole 68 defining the branch 53 and reaches the chamber 75 defining the branch 52 and housing the stator 3. The first fluid flows through stator 3 and cools stator 3 itself. Subsequently, the first fluid flows through the hole 85 and the helical groove 80 defining the branch 54 of the cooling circuit 50, and passes through the duct 90 defining the branch 55 of the cooling circuit 50 until it returns to the duct 67 of the branch 51. In greater detail, the first fluid flowing along the groove 80 transfers heat to the second fluid flowing along the groove 115. More precisely, the first fluid is at a first temperature value when it flows along the hole 85 and is at a second temperature value lower than the first temperature value when it flows along the conduit 90. From an examination of the electric motor 2 made according to the present invention, the advantages that it allows to obtain are evident. In particular, the cooling circuit 50 removes heat from the stator 3 and the rotor 4, and comprises, in turn, a branch 51 housed inside the rotor 4 and shaped like a propeller. In this way, the centrifugal force acting on the first fluid following the rotation of the rotor 4 is used, thanks to the helical shape of the branch 51, to generate an axial thrust on the first fluid itself directed in the direction oriented from the duct 67 to the duct 68. This axial thrust ensures the circulation of the first long fluid inside the cooling circuit 50 and allows the inevitable pressure drops present along the cooling circuit 50 itself to be overcome. It is thus possible to avoid the use of pumps dedicated to the circulation of the first fluid within the cooling circuit 50 with consequent advantages in terms of increased torque and power density, and reduction of weight and size of the electric motor 2. The first fluid flowing along the cooling circuit 60 is returned along the branch 54 from the third temperature value to the fourth temperature value lower than the third temperature value, and can thus effectively cool the rotor 4 and the stator 3 again along the respective branches 51, 52, without requiring the use of additional heat exchangers. This further increases the torque and power density of the electric motor, and further reduces its weight and size. The branch 51 of the cooling circuit 50 along which the first fluid cools the rotor 4 is interposed between the branch 54 along which the first fluid is cooled by the second fluid and the branch 52 along which the first fluid cools the stator 3. In this way, the first fluid is at a lower temperature when it removes heat from rotor 4 than when it removes heat from stator 3. This allows more heat to be removed from rotor 4, which is at a higher temperature due to the presence of the permanent magnets. The cooling circuit 50 is, moreover, completely housed inside the electric motor 2, thus forming with it a single assembly that can be removed and installed from the motor vehicle 1 without having to act on components other than the inlet port 110 and the outlet port 111. Thanks to the fact that the first fluid is a dielectric oil, there is no risk of short circuits with the electrical components of rotor 4. Finally, it is clear that modifications and variations can be made to the electric motor 2 made according to the present invention which, however, do not go beyond the scope of protection defined by the claims.

Claims

CLAIMS 1.- Electric motor (2) for a motor vehicle (1), comprising: - a stator (4) fixed with respect to an axis (A); - a rotor (3) rotating around said axis (A) with respect to said stator (4) and provided with a plurality of permanent magnets; and characterised by the fact that it comprises a first cooling circuit (50) which can be passed through by a first heat-transfer fluid and which is thermally coupled, in use, with said stator and rotor (4, 3) to remove heat from them; said first cooling circuit (50) comprising, in turn, a first branch (51) housed inside said rotor (4) and shaped like a propeller.

2. - Electric motor according to claim 1, characterised in that said first cooling circuit (50) comprises a second branch (52) passing through said stator (3) and thermally coupled with said stator (3) to remove heat from it; said second branch (52) being consecutive to said first branch (51), with reference to a normal direction of advancement of said first fluid inside said first cooling circuit (50).

3. - Electric motor according to claim 2, characterised by the fact that it comprises a casing (30) housing the said rotor (4) and stator (3); the said first cooling circuit (50) comprising a third branch (54) passing through the said casing (30); the said third branch (54) being consecutive to the said second branch (52), with reference to a normal direction of advancement of the said first fluid inside the said first cooling circuit (50).

4. - Electric motor according to any of the preceding claims, characterised by housing a quarter of a branch (106) of a second cooling circuit (60) which can be passed through by a second heat transfer fluid and is thermally coupled, in use, with the said first cooling circuit (50) to remove heat from them.

5. - Electric motor according to claim 4, characterised in that said fourth branch (106) extends inside said casing (30) and is thermally coupled with said third branch (54) of the first cooling circuit (50).

6. - Electric motor according to claim 5, characterised in that said fourth branch (106) coaxially surrounds said third branch (54).

7. - Electric motor according to claim 5 or 6, characterised in that said third and fourth branches (106, 54) are shaped as respective coaxial propellers.

8. - Electric motor according to any of the preceding claims, characterised in that said second branch (52) has a prevalent extension parallel to said axis (A).

9. - Electric motor according to any of claims 4 to 8, characterised in that the said casing (30) comprises: - a tubular body (31) coaxially surrounding the said stator and rotor (3, 4) and defining an inlet and an outlet (110, 111) for the said second fluid; and - a first and a second flange (32, 33) arranged at respective axial ends of the said tubular body (31); the said third and fourth branches (106, 54) extending inside the said tubular body (30); the said second flange (33) housing a fifth branch (55) of the said first cooling circuit (50); the said fifth branch (55) being fluidically connected between the said third branch (54) and the first branch (51). 10.- Electric motor according to any of claims 4 to 9, characterised in that; - said rotor (4) comprises at least one hole (68) radial to said axis (A), and a helical groove (66) defining at least part of said first branch (51) and in fluid communication with said first hole (68); - said casing (30) and said rotor (4) define a first annular chamber (70) in fluid communication with a hole (68); and - said casing (30) defines a second annular chamber (75), housing said stator (3) and in fluid communication with said first chamber (70); the said second chamber (75) defining, at least in part, the said second branch (52), and the said third chamber (70) and the said hole (68) defining, at least in part, a fifth branch (55) of the said first cooling circuit (50) fluidically interposed between the said first branch (51) and third branch (5). 11.- Electric motor according to any of the preceding claims, characterized in that said first fluid is different from said second fluid, in particular said first fluid is oil and said second fluid is a mixture comprising at least partly water; and / or in that said first fluid is dielectric. 12 . - Motor vehicle comprising: - an electric motor (2) according to any of claims 4 to 11; said second cooling circuit (60) further comprising a heat exchanger (102) external to said electric motor (2) and fluidically connected to said fourth branch (106); said heat exchanger (102) in turn comprising a second inlet suitable for receiving said second fluid at a first temperature and a second outlet suitable for supplying said second fluid at a second temperature lower than said first temperature.